An essential characteristic of advanced practice nurses is the use of theory in practice. Clinical nurse specialists apply theory in providing or directing patient care, in their work as consultants to staff nurses, and as leaders influencing and facilitating system change. Knowledge of technology and pharmacology has far outpaced knowledge of how to facilitate health behavior change, and new theories are needed to better understand how practitioners can facilitate health behavior change. In this article, the Integrated Theory of Health Behavior Change is described, and an example of its use as foundation to intervention development is presented. The Integrated Theory of Health Behavior Change suggests that health behavior change can be enhanced by fostering knowledge and beliefs, increasing self-regulation skills and abilities, and enhancing social facilitation. Engagement in self-management behaviors is seen as the proximal outcome influencing the long-term distal outcome of improved health status. Person-centered interventions are directed to increasing knowledge and beliefs, self-regulation skills and abilities, and social facilitation. Using a theoretical framework improves clinical nurse specialist practice by focusing assessments, directing the use of best-practice interventions, and improving patient outcomes. Using theory fosters improved communication with other disciplines and enhances the management of complex clinical conditions by providing holistic, comprehensive care.